[GHC] #12844: No Skolem Info with PartialTypeSignatures

[GHC]

#12844: No Skolem Info with PartialTypeSignatures
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        Reporter:  crockeea          |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.0.2
       Component:  Compiler          |              Version:  8.0.1
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Compile-time      |            Test Case:  partial-
  crash or panic                     |  sigs/should_compile/T12844
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by bgamari):

 * status:  merge => closed
 * resolution:   => fixed
 * milestone:   => 8.0.2


@@ -3,1 +3,1 @@
- {{{
+ {{{#!hs

New description:

 The following program triggers a panic:

 {{{#!hs
 {-# LANGUAGE DataKinds             #-}
 {-# LANGUAGE PartialTypeSignatures #-}
 {-# LANGUAGE PolyKinds             #-}
 {-# LANGUAGE TypeFamilies          #-}
 {-# LANGUAGE TypeOperators         #-}

 barWraper :: ('(r,r') ~ Head rngs, Foo rngs) => FooData rngs
 barWraper = bar

 bar :: (_) => FooData rngs
 bar = foo

 data FooData rngs

 class Foo xs where foo :: (Head xs ~ '(r,r')) => FooData xs

 type family Head (xs :: [k]) where Head (x ': xs) = x
 }}}

 {{{
 > ghci NoSkolem.hs
 [1 of 1] Compiling Main             ( NoSkolem.hs, NoSkolem.o )

 NoSkolem.hs:8:13: error:ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         No skolem info: k_aYV[sk]
 }}}

 I haven't tested with 8.0.2 or head.

--

Comment:

 Merged to `ghc-8.0` as 4212674ba92971734eec064809f8e1a45bca992a.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12844#comment:3>
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